Transmission line optimization for targeting impedance or group index performance, such as for traveling wave modulator applications, may require tuning of the signal width and signal-to-ground gap for legacy transmission line designs. This tuning may simultaneously impact a variety of parameters such as the access resistance to a load, transmission line inductance, transmission line capacitance, etc. Often, fine control of transmission line parameters may be required for a high-performance traveling wave device. However, this fine control may present a challenge given the complex coupling between key parameters and physical geometric parameters that may exist in legacy designs.
Additionally, when driving an un-terminated lumped-element component (such as may be the use case for a ring modulator), access resistance to the load may be considered a critical parameter as related to component response time due to the resistance/capacitance (RC) time constant of the system. Often, there may be geometrical constraints that limit the proximity of the physical contact to the load, which in turn may impact access resistance of the transmission line. Often, bias point control may be realized with a heater that is used to tune the optical phase-offset of the transmission line. The inclusion of the heater may create size-limitations in the transmission line in order to optimize heater efficiency and resistance.